1. Field of the Invention
The present invention relates to a receiving device and a receiving method for receiving data via a power line transmission network which transmits the same data with the same timing in parallel via a plurality of communication channels by means of superposition on AC power, in which a communication channel used to receive the data is selected on the basis of channel usage periods measured for the respective communication channels.
The present invention also relates to a transmitting method for transmitting data such that transmission data is generated by converting input data into packets and outputting each same packet repeatedly a plurality of times, and the transmission data is transmitted via a plurality of communication channels at the same time by means of superposition on AC power.
2. Description of the Related Art
In recent years, a power line transmission/reception system has been proposed and realized, for transmitting/receiving information such as an audio or video signal via a power line used to distribute commercial AC power to rooms in a home. An example of a power line transmission technique is disclosed in U.S. patent application Ser. No. 09/247,943 field on Feb. 11, 1999, which is incorporated herein by reference. In such a power line system, for example, a transmission signal is generated by modulating an audio signal or a video signal, and the resultant transmission signal is superimposed on commercial AC power distributed via a power line. In a receiving device, the transmission signal component superimposed on the commercial AC power is extracted and then demodulated thereby reproducing the original audio signal or video signal.
In general, not only a power line transmission/reception system but also other devices such as an electric lamp and various types of electronic devices are connected to a power line. In the power line transmission/reception systems, therefore, there is a rather high possibility that noise generated from electronic devices connected to the power line interferes with reception/reception.
One known technique of avoiding the above problem in the power line transmission/reception systems is to transmit the same information via a plurality of channels. In this technique, the same audio or video signal is modulated using a plurality of carriers having different frequencies and transmitted via different channels corresponding to the carrier frequencies. That is, the same information is transmitted from a transmitting device via a plurality of channels which are obtained in the above-described manner.
In a receiving device, a channel which provides a best reception, that is, which has a highest channel quality, is selected from the plurality of channels and is used for transmission of the information.
In this technique in which the same information is transmitted via the plurality of channels, even when a channel with a certain frequency is influenced by noise generated by another device, the receiving device can receive the information under a good condition by selecting a channel with another frequency which is not influenced by the noise.
The channel selection may be performed manually by a user. It is also known in the art to construct a receiving device such that the channel is automatically switched without needing a manual operation when degradation in the condition of the current channel is detected.
FIG. 1 illustrates an example of a manner in which the channel is switched in a receiving device having such an automatic channel switching capability.
In this example shown in FIG. 1, transmission is performed using three channels #1, #2, and #3.
When the channel #1 is used for reception, if a reception error is detected, that is, if the reception condition of the channel #1 becomes worse than an allowable level, the receiving device automatically switches the reception channel to the channel #2. If a reception error is detected during the reception using the channel #2, the reception channel is switched to the channel #3.
If a further reception error is detected during the reception using the channel #3, the reception channel is switched to channel #1 which was used first.
That is, the channel is switched in a predetermined fixed order, such as #1xe2x86x92#2xe2x86x92#3xe2x86x92#1 . . . , each time a reception error occurs.
However, the conventional channel switching technique described above with reference to FIG. 1 has the following problems.
When a channel is switched to another channel in response to detection of a reception error, it is not assured that a good reception condition is obtained in the new channel. If the new channel does not provide good reception, the channel is further switched to another channel until a good reception condition is obtained. Thus, in some cases, it takes a long time to reach a good channel. That is, a communication error or a bad communication condition can often occur over a rather long period of time.
Herein, let us assume that a channel which provides the best reception quality is now being used and all the other channels are under steady bad reception conditions.
The current channel having the best reception quality can temporarily fall into a bad reception state due to sudden noise. However, in such a case, the channel should not be switched to another channel, and the current channel should be maintained.
However, in the channel switching technique shown in FIG. 1, detection of a reception error always causes switching from the current channel to a predetermined next channel, and thus, in this specific example, the current channel which provides the best reception is switched to the next channel which is steadily in the bad state and further to another bad channel. Thus, it takes a long time to return to the best channel.
As described above, the conventional technique has the problem that the simple channel switching in the fixed order does not allow the channel to be properly switched depending upon the actual reception conditions of the respective channels.
According to an aspect of the present invention, there is provided a receiving device for receiving data via a power line transmission network which transmits the same data with the same timing in parallel via a plurality of communication channels by means of superposition on AC power, the receiving device comprising: receiving means for extracting data superimposed on AC power from a particular channel of the network thereby receiving said data; timer means for measuring a channel usage period during which a communication channel is used by the receiving means to receive data; storage means for storing the channel usage period measured by the timer means, for each communication channel; calculation means for calculating the mean channel usage period of each communication channel from the channel usage periods stored in the storage means; and control means which controls the storage means so as to store the channel usage period measured by said timer means for each communication channel, and which controls the receiving means so as to select a communication channel used to receive data on the basis of the mean channel usage periods of the respective communication channels calculated by the calculation means and so as to receive the data using the selected channel.
According to another aspect of the present invention, there is provided a transmitting device for transmitting input data via a power line transmission network which has a plurality of communication channels and which transmits data by means of superimposing data upon AC power, the transmitting device comprising: compression means for compressing the input data; packet conversion means for converting the data compressed by the compression means into packets each having a predetermined length of data;. transmitting means for transmitting the data converted into packets by the packet conversion means via the plurality of communication channels at the same time.
According to still another aspect of the present invention, there is provided a receiving method for receiving data via a power line transmission network which transmits the same data with the same timing in parallel via a plurality of communication channels by means of superposition on AC power, the receiving method comprising the steps of: extracting data superimposed on AC power from a particular channel of the network thereby receiving the data, and measuring a channel usage period during which a communication channel is used to receive the data; when a communication failure is detected during the reception of the data, calculating the mean channel usage period of the particular channel from the channel usage period measured during the current receiving operation and from the channel usage periods of the particular channel measured in the past; selecting a communication channel to be used, on the basis of the calculated mean channel usage period and the mean channel usage periods calculated for the other respective communication channels.